It's derived from LIDAR scans. https://www.usgs.gov/ngp-standards-and-specifications/elevation-derived-hydrography-and-national-hydrography-datasets https://ww

It's derived from LIDAR scans. https://www.usgs.gov/ngp-standards-and-specifications/elevation-derived-hydrography-and-national-hydrography-datasets https://www.usgs.gov/ngp-standards-and-specifications/elevat... I'm not sure it's their best product for elevation anymore, but USGS also publishes 3dep, which is a unified layer of the best available elevation data for the US.